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Experimental and theoretical calculations confirm, for the first time, the existence of two different kinds of electronic structures of a surface complex formed by a particular molecule bonded to charged metal electrodes, clusters, or nanoparticles. Surface-enhanced Raman scattering (SERS) of cyanine adsorbed on a silver electrode shows three regions, which are selected by the electrode potential and characterized by the differentiated response of the vibrational wavenumbers of the ?(CN) stretching band to the electrode potential. The combination between the experimental SERS and DFT calculations has allowed for relating the three regions to chemisorbed (C-hybrid) and physisorbed (P-hybrid) surface complexes, where cyanide is bonded through the carbon on top of a single silver atom of the surface and to bidentate species, respectively. The electrode potential selects one or another type of electronic structure of the surface complex, which are of different natures and with a differentiated response to the applied potential. The electric potential tunes smoothly the wavenumbers, bond energies, and injected charges of the P-hybrid at more negative potentials than that of the zero charge of the electrode, but the very strong C-hybrid prevents significant changes of these properties at positive excesses of charge. The existence of the dual electronic structure of metal-molecule interfaces might require reinterpreting experiments that are usually discussed by resorting to, for instance, the reorientation of the adsorbate, the formation of complexes with different stoichiometries, the existence of nonequivalent local sites on the surface, or to instrumental artifacts.

10 pags., 7 figs., In this work, we explore the use of surface-enhanced Raman scattering (SERS) on silver (Ag) nanoparticles for the detection of triazine pesticide atrazine and prometryn as well as their degradation products. This tecnique was used to monitor the pesticide degradation both in the commercial samples as well as by the effects of heat and humidity. We have studied the adsorption affinity of these pesticides as well as their degradation products on the employed SERS substrates in order to check the optimal conditions in the detection of both the original pesticide and their degradation products. The presence of these products in triazine pesticides with high solubility in water is of great interest for the human health, but what's even more important is the fact that the pesticide degradation can be favored by very mild conditions of humidity, temperature, and pH, thus leading to high levels of structural modifications, which produce other final compounds with an even higher impact on both human health and environment., Conselho Nacional de Desenvolvimento Científico e Tecnológico Coordenação de Aperfeiçoamento de Pessoal de Nível Superior FAPESP. Grant Numbers: 2013/14262‐7, 2016/0634‐0 Ministerio de Economía y Competitividad. Grant Numbers: CTQ2015‐65816‐R, FIS2017‐84318‐R

The photodissociation channels of nitrosobenzene (PhNO) induced by a 255 nm photolytic wavelength have been studied using the complete active space self-consistent method and the multistate second-order multiconfigurational perturbation theory. It is found that there exists a triplet route for photodissociation of the molecule. The reaction mechanism consists of a complex cascade of nonadiabatic electronic transitions involving triple and double conical intersections as well as intersystem crossing. Several of the relevant states (S2, S4, and S5 states) correspond to double excitations. It is worth noting that the last step of the photodissociation implies an internal conversion process. The experimentally observed velocity pattern of the NO fragment is a signature of such a conical intersection.

This work presents a synergistic approach to boost plasmon- or surface-enhanced Raman scattering (SERS) by combining molecular and electrical modulators that fine-tune the electronic structure of metal–molecule interfaces, especially the charge transfer (CT) states, allowing molecular resonances. Paraquat (PQ2+) was interfaced with nanopillar SERS substrates whose surface excess of charge was modulated by intercalating anionic Au complexes (AuCl4−, Au(CN)2−) as well as by applying external electric potentials. Such concurrent dual modulation tuned the energy of the CT states of the substrate–anion–PQ2+ triads in resonance with the excitation laser, resulting in a large enhancement of the PQ2+ SERS bands. The results point to a novel coherent through-bond CT contribution of SERS, analogous to the superexchange mechanism for electron transfer in donor–bridge–acceptor systems. The large amplification enables high sensitivity for detecting PQ2+ and ultimately enables the on-site detection of PQ2+ in unprocessed real samples (coffee drink). This study accounts for new physicochemical variables affecting electron transfer processes in nanostructured metal–molecule interfaces and provides a path for further exploring chemical strategies for greater Raman enhancement and for developing ultrasensitive Raman platforms.

13 pags., 6 figs., 1 tab. -- This article belongs to the Special Issue Nanomaterials in Surface-Enhanced Raman Spectroscopy, Silver nanoparticles functionalized with thiolated β-cyclodextrin (CD-SH) were employed for the detection of bisphenols (BPs) A, B, and S by means of surface-enhanced Raman spectroscopy (SERS). The functionalization of Ag nanoparticles with CD-SH leads to an improvement of the sensitivity of the implemented SERS nanosensor. Using a multivariate analysis of the SERS data, the limit of detection of these compounds was estimated at about 10−7 M, in the range of the tens of ppb. Structural analysis of the CD-SH/BP complex was performed by density functional theory (DFT) calculations. Theoretical results allowed the assignment of key structural vibrational bands related to ring breathing motions and the inter-ring vibrations and pointed out an external interaction due to four hydrogen bonds between the hydroxyl groups of BP and CD located at the external top of the CD cone. DFT calculations allowed also checking the interaction energies of the different molecular species on the Ag surface and testing the effect of the presence of CD-SH on the BPs’ affinity. These findings were in agreement with the experimental evidences that there is not an actual inclusion of BP inside the CD cavity. The SERS sensor and the analysis procedure of data based on partial least square regression proposed here were tested in a real sample consisting of the detection of BPs in milk extracts to validate the detection performance of the SERS sensor., This research was supported by the Italian Ministry of Health, Rome, Italy (IZSLT11/17 RC) (G.S., B.N., and C.F.), MINECO/FEDER (FIS2017-84318-R) (S.S.C.), and by Junta de Andalucía/FEDER (UMA18-FEDERJA-049 and P18-RT-4592) (J.C.O.).

The detection of emerging contaminants in the aquatic environment, such as ibuprofen and caffeine, was studied by means of surface-enhanced Raman spectroscopy (SERS) using Ag nanoparticles (AgNPs) synthesized with &beta, cyclodextrin (&beta, CD) as a reducing agent. The effect on the SERS signal of different molar ratios of Ag+/&beta, CD in the synthesis route and the aging process of AgNPs were investigated by using trans-cinnamic as a test molecule. The SERS effectiveness of these &beta, cyclodextrin colloids (Ag@&beta, CD) was also checked and compared with that of other silver sols usually employed in SERS synthesized by using other reducing agents such as citrate, borohydride and hydroxylamine. All the synthesized SERS substrates were characterized by different techniques. The experimental results indicate that Ag@&beta, CD with the more diluted Ag+/&beta, CD molar ratio showed the best SERS signal, enabling detection at trace concentrations of 0.5 &micro, M in the case of trans-cinnamic acid. The Ag@&beta, CD sols also showed the best sensitivity for detecting ibuprofen and caffeine, reaching the lowest limit of detection (0.1 mM). The proposed synthetic route for Ag@&beta, CD sols provides an improved SERS substrate for detecting organic pollutants with better performance than other standard silver sols.

Applied electric potentials tune SERS wavenumbers due to vibrational Stark effect, but some modes of 4CNB- show two differentiated regions, being redshifted at more negative potentials than the potential of zero charge of the electrode but remain unshifted at positive potentials. DFT calculations have been carried out for a model where 4CNB- is linked through the carboxylate [Agnq-OOC(4CNB-)]q-1 or the nitrile [Agnq-NC(4CNB-)]q-1 to stick-like silver clusters [Agn]q with different densities of charge (qeff =q/n). The comparison between calculated and experimental wavenumber shifts points out that 4CNB- is always adsorbed through the carboxylate. The dual behaviour of the wavenumbers is due to the existence of two types of electronic structure of the metal-molecule hybrid. Physisorbed (P-hybrid, repulsive) or chemisorbed (C-hybrid, attractive) surface complexes are selected by the sign of the surface excess of charge of the electrode. The electronic structure of weakly bonded P-hybrid is very sensitive to the voltage and their wavenumbers are continuously shifted, while the wavenumbers of the strong C-hybrid remain almost unshifted. This result proves the dual nature of the electronic structure of molecules bonded to charged metal electrodes or nanoparticles which can be responsible of the qualitative changes observed in electrochemical or molecular electronics experiments.

Background:The impact of the ubiquitous dietary phenolic compound p-coumaric acid on human breast cancer cells was assessed, through a multidisciplinary approach: Combined biological assays for cytotoxicity evaluation and biochemical profiling by Raman microspectroscopic analysis in cells. Methods: Para-coumaric acid was shown to exert in vitro chemoprotective and antitumor activities, depending on the concentration and cell line probed: a significant anti-invasive ability was detected for the triple-negative MDA-MB-231 cells, while a high pro-oxidant effect was found for the estrogen- dependent MCF-7 cells. A striking cell selectivity was obtained, with a more noticeable outcome on the triple-negative MDA-MB-231 cell line.Results:The main impact on the cellular biochemical profile was verified to be on proteins and lipids, thus justifying the compound´s anti-invasive effect and chemoprotective ability.Conclusion:p-Coumaric acid was thus shown to be a promising chemoprotective/chemotherapeutic agent, particularly against the low prognosis triple-negative human breast adenocarcinoma.

The reaction mechanisms for the carbon-based acid catalytic conversion of 2-butanol into dehydration and dehydrogenation products (alkene derivatives and ketone) have been theoretically studied by assuming that the acid site is a dihydrogen phosphate group bonded to one of the carbon atoms of the central ring of anthracene. The structural model of the active site of the surface of the catalyst reproduces properly the experimental results. Kinetic and thermodynamic magnitudes have been obtained by using standard expressions of Eyring’s transition-state theory and statistical thermodynamics. Interpretation of the calculations (molecular charges, geometries, and energies) demonstrates that the dehydration reaction process is an E2 mechanism (one-step reaction) with strong character of E1 mechanism (two-step reaction). The study of the mechanism has been carried out by applying density functional theory with the metaexchange–correlation functional M06-2X. The reactants and products connected by the respective...

Aryl azides photochemistry is strongly dependent on the substituent relative position, as has been studied by time resolved resonant Raman (TR3) spectroscopy for 4-methoxyphenyl azide and its isomer 3-methoxyphenyl azide. When irradiated at 266 nm, the former results in 4,4’-dimethoxyazobenzene whereas the latter forms 1,2-didehydroazepine. It is proposed that the key step of the reactions is the formation of a nitrene derivative. Recently, it has been proposed by us that nitrenes might have a relevant role in the Surface-Enhanced Raman Scattering (SERS) of p-aminothiophenol, however, the molecular mechanism is not well known in neither of these cases. Therefore, we studied the photodecomposition of 4-methoxyphenyl azide using multiconfigurational self-consistent field methods (MC-SCF) with the CAS-SCF and MS-CASPT2 approximations and calculated the resonant Raman spectra of the relevant species using a multi-state version of Albrecht’s vibronic theory. The results propose that the reaction follows a two steps sequence after irradiation at 266 nm: an intersystem crossing 21A’/23A’’ which decays through a 21A’/21A’’ conical intersection producing molecular nitrogen and triplet 4-methoxyphenyl nitrene in its ground state. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.

Despite the growing interest in the potential electrochemical applications of both aluminium and ionic liquids in batteries, the microstructure of mixtures of trivalent salts and these dense ionic environments is completely unknown. In this work, the solvation of Al3+ cations in highly dense ionic solvents is investigated. For this purpose, molecular dynamics simulations of mixtures of a protic ionic liquid, ethylammonium nitrate (EAN), with aluminium nitrate (Al(NO3)3), both in bulk and confined between graphene walls, are performed. Several structural quantities of the system are calculated for different salt concentrations, such as densities, radial distribution functions, structure factors, coordination numbers and hydrogen bonds for the bulk mixture and ionic density profiles for the confined ones. Moreover, vibrational density of states is calculated for the salt cations, both in bulk and when close to the walls. The results obtained are analyzed and compared to those for mixtures of EAN with monovalent and divalent salts, in order to probe the influence of the salt cation charge on the system's properties. Finally, ab initio density functional theory calculations were performed in order to analyze the structure of the Al3+-ligand complexes, and their predictions for the Raman spectrum are compared both to the corresponding experimental one and the one coming from molecular dynamics simulations. According to our calculations, [Al(NO3)6]3- octahedral complexes do not significantly change the microstructure of the mixtures relative to those of Mg2+-based ones.

Electrochemical surface-enhanced Raman scattering (SERS) of the cruciform system 1,4-bis((E)-2-(yridine-4-yl)vinyl)naphthalene (bpyvn) was recorded on nanostructured silver surfaces at different electrode potentials by using excitation laser lines of 785 and 514.5 nm. SERS relative intensities were analyzed on the basis of the resonance Raman vibronic theory with the help of DFT calculations. The comparison between the experimental and the computed resonance Raman spectra calculated for the first five electronic states of the Ag2-bpyvn surface complex model points out that the selective enhancement of the SERS band recorded at about 1600 cm&minus, 1, under 785 nm excitation, is due to a resonant Raman process involving a photoexcited metal-to-molecule charge transfer state of the complex, while the enhancement of the 1570 cm&minus, 1 band using 514.5 nm excitation is due to an intramolecular &pi, &rarr, &pi, * electronic transition localized in the naphthalenyl framework, resulting in a case of surface-enhanced resonance Raman spectrum (SERRS). Thus, the enhancement of the SERS bands of bpyvn is controlled by a general chemical enhancement mechanism in which different resonance processes of the overall electronic structure of the metal-molecule system are involved.

In the present work, we demonstrate that the formation of triplet and singlet phenylnitrene, when arises from the photodissociation of phenyl azide, fulfills El-Sayed's rules or the electronic angular momentum conservation law. It is shown that the singlet-triplet inversion of phenylnitrene via the vibronic coupling mechanism is not an effective process. In contrast, it is found that there exist two independent dissociation channels that yield alternatively singlet and triplet phenylnitrene. Therefore, a proposed mechanism that violates the angular momentum low is avoided. The clue of the photoreaction lies in the conjunction (energetic and spatial) of two crossing points in a very narrow region of the multidimensional space: (i) an intersystem crossing (ISC1) and (ii) a conical intersection (CI1). The geometrical separation between these two crossing geometries is only 0.016 A measured in Cartesian coordinates, and the respective energy difference is 2 kcal/mol. This work has been performed by application of the complete active space self-consistent field and multiconfigurational second-order perturbation method.

A Surface-Enhanced Raman Scattering (SERS) spectrum of 4-cyanopyridine (4CNPy) was recorded on silver plasmonic nanoparticles and analyzed by using Density Functional Theory (DFT) calculations. Two simple molecular models of the metal&ndash, 4CNPy surface complex with a single silver cation or with a neutral dimer (Ag+&ndash, 4CNPy, Ag2&ndash, 4CNPy), linked through the two possible interacting sites of 4CNPy (aromatic nitrogen, N, and nitrile group, CN), were considered. The calculated vibrational wavenumbers and intensities of the adsorbate and the isolated species are compared with the experimental Raman and SERS results. The analysis of the DFT predictions and the experimental data indicates that 4CNPy adsorbs preferentially on neutral/charged active sites of the silver nanoparticles through the nitrogen atom of the aromatic ring with a perpendicular orientation.

9 pags. 6 figs., In this work, the adsorption of a type of cruciform system integrated by an anthracene central part and two side chains with a pyridine-vinyl structure (DPAC) was studied on plasmonic nanoparticles of silver and gold. The adsorption was investigated by surface-enhanced Raman scattering, which reveals very valuable information about both the interaction mechanism and the molecular orientation. The highest Raman enhancement was measured on Ag nanostars due to the combination of gaps and tips in these nanostructures. The changes observed in the surface-enhanced Raman scattering spectra indicate that the adsorption of DPAC on the metal is bifunctional in the case of Ag and Au nanoparticles. Considering that the Raman signals enhancement is several orders of magnitude higher in gaps in relation to regions out of these areas, it is estimated that the enhancement ability of DPAC in Ag nanostars is so high that it allows the detection of a concentration close to pM., This work was supported by MINECO under FIS2014‐52212‐R and CTQ2015‐65816‐R projects. P. Leyton acknowledges to the project FONDECYT 1140810 as wellas the FONDEQUIP EQM130170 project from CONICYT.E. Imbarack acknowledges the financial supports fromBeca Doctorado Nacional N°21140360 CONICYT.

The electron donor-acceptor properties of 9,10-bis((

Surface-enhanced Raman scattering of thiobenzoic acid and thiobenzamide have been recorded on three different silver colloids in order to find the chemical species responsible for the spectra and to detect differences in the adsorption with respect to their oxygen counterparts, benzoic acid and benzamide, respectively. Very significant and unexpected shifts of opposite sign between the Raman and SERS wavenumbers have been detected. By comparing the experimental and DFT calculated wavenumbers, it can be concluded that the acid is bonded to the metal as thiobenzoate through the sulfur atom with unidentate coordination. SERS spectra of thiobenzamide can be explained by assuming that it is adsorbed as azanion, like in the case of benzamide, linking to the metal through the sulfur and nitrogen atoms of the ionized thiocarboxamide group. In order to support these conclusions, B3LYP/LanL2DZ force field calculations for different complexes of silver cations with the thiobenzoate anion, the neutral thiobenzamide as well as its azanion have been carried out. Additionally, the 8a;?ring mode is the most enhanced band in the SERS of both adsorbates pointing to the participation of a metal-to-molecule resonant charge transfer mechanism.

The differences between alternative approaches for quantifying the complex effect of the electronic structure of charged metal–molecule hybrids in SERS (the so-called chemical enhancement mechanism) are highlighted. The discussion is focussed on the predictions obtained by using different methodological tools for modelling the role of the electrode potential in the SERS relative intensities. Finite electric fields are used in the commented paper for this purpose, but we have found some inconsistences in the results and the method for calculating the Raman intensities is not made sufficiently clear, which prevents the assessment of the results.

Raman and SERS spectra of benzaldehyde (Bz-CHO) and chromone-3-carboxaldehyde (Ch-CHO) on silver colloids have been analyzed, being subsequently compared to the spectra of the corresponding acids. In the SERS spectra of both aldehydes, the band corresponding to the ν(CO) stretching mode of the carboxaldehyde group at ca. 1700 cm−1 is missing, while a new band at 1350–1400 cm−1, characteristic of the symmetric stretching mode of carboxylate group, is appearing in both cases. These results point out that aldehydes are oxidized to their corresponding acids when adsorbed on silver nanoparticles. This conclusion has been confirmed by means of HPLC-MS analysis and supported on the basis of DFT calculations. Copyright © 2016 John Wiley & Sons, Ltd.

The effect of adsorbate concentration on the potential dependent SERS spectra of p-aminothiophenol (pATP) recorded on a silver electrode has been studied using NaClO4 as electrolyte. Multiconfigurational second-order perturbation calculations (MS-CASPT2) have been performed in order to help the analysis of the experimental results by computing resonance Raman spectra of selected structural models of the metal–adsorbate surface complex. In order to avoid as far as possible any photochemical reaction, a long wavelength exciting line of 785 nm is used in the experiments. It is found that the spectra are dependent on adsorbate concentration and dominated by a resonant charge transfer (CT) mechanism, where the charge is always transferred from the adsorbate to the metal. The relative SERS enhancements are due to Franck–Condon factors related to the CT process, and there are not intensified bands through Herzberg–Teller contributions. Furthermore, the Raman signals of the SERS recorded at low concentration aris...

Photochemistry of 3- and 4-methoxyphenyl azide at 266 nm has been studied by means of the complete active space self-consistent field (CASSCF) and multi-configurational second-order perturbation (MS-CASPT2) methods. Minima and interstate crossing points have been optimized using the CASSCF method. The calculations predict that the key step of the photolysis of both azides is a non-radiative process. However, an important difference is found when we compare the reactivity of both isomers of azide, deactivation of 3-methoxyphenyl azide (1) can occur via two reaction channels (internal conversion or intersystem crossing), which lead to formation of the dimer of 2H-azepine derivative (2a) and 3,3'-dimethoxyazobenzene (2b). In contrast, deactivation of 4-methoxyphenyl azide (3) takes place via a singlet to triplet intersystem crossing, which leads to formation of 4,4'-dimethoxyazobenzene (4). After initial deactivation, both isomers follow a cascade of surface crossings until they reach the final nitrenes, respectively. The reference active space for the two azides is 14 electrons in 13 orbitals and comprises the six π-type orbitals of the aromatic ring plus four σ-(N-N2) and five π-type orbitals of the -N3 moiety.

9 pags., 6 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 3.0, The electron donor-acceptor properties of 9,10-bis((E)-2-(pyridin-4-yl)vinyl) anthracene (BP4VA) are studied by means of surface-enhanced Raman scattering (SERS) spectroscopy and vibronic theory of resonance Raman spectroscopy. The SERS spectra recorded in an electrochemical cell with a silver working electrode have been interpreted on the basis of resonance Raman vibronic theory assisted by DFT calculations. It is demonstrated that the adsorbate-metal interaction occurs through the nitrogen atom of the pyridyl moiety. Concerning the electron donor-acceptor properties of the adsorbate, it is shown that the charge transfer excited states of BP4VA are not optically active, in contrast, an internal transition to an excited state of BP4VA, which is localized in the anthracene framework, is strongly allowed. The charge transfer states will be populated by an ultrafast non-radiative process, that is, internal conversion. Thus, irradiation of BP4VA interacting with an appropriate surface creates an effective charge separation., This research has been supported by the Spanish Ministerio de Economıa y Competitividad (Projects: FIS2017-84318-R and CTQ2015-65816-R). EI and PL acknowledges the financial supports from the projects FONDECYT 1140810 and Beca Doctorado Nacional No. 21140360 from CONICYT. The authors thank Rafael Larrosa and Dar´ıo Guerrero for the technical support in running the calculations and the SCBI (Supercomputer and Bioinformatics) center of the University of Malaga for computer resources.

Carbendazim (MBC) is a fungicide widely used in agriculture, and there are serious concerns regarding the health risks that could be caused by this fungicide. Here, we explore its ultrasensitive detection by surface-enhanced Raman scattering (SERS). First, to obtain maximum SERS signal, the adsorption of the target molecule onto metallic surface is essential. Therefore, we study the adsorption of the MBC onto the nanoparticle surface by SERS under different experimental conditions, such as different synthesis methods of nanoparticle, variable excitation wavelength, and fungicide concentration with the aim to detect MBC at low concentrations. Experiments are carried out with three kinds of colloidal nanoparticles: Ag and Au reduced by citrate and Ag reduced by hydroxylamine. However, mainly Ag colloids are highly efficient in the SERS detection of MBC. In addition, theoretical calculations of MBC Raman spectrum and that of the surface complex are used to help with the understanding the mechanisms responsible for the interaction between MBC and Ag. Ultraviolet–visible absorption spectroscopy showed displacement to the red of the plasmon resonance of Ag colloid in the presence of MBC. Copyright © 2015 John Wiley & Sons, Ltd.

DFT calculations predict that plasmon-like excitations in small metal clusters are able to selectively modify the relative intensities of specific SERS bands of adsorbed molecules. These electronic resonances provide new kinds of SERS selection rules which can explain the huge enhancement of mode 9a of pyridine in the spectra recorded at negative electrode potentials.

A painting bearing the signature “Picasso” was investigated and its components – pigments and binders – were characterised using micro-Raman spectroscopy (mRS) combined with other analytical techniques such as Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM/EDX), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Gas Chromatography-Mass Spectrometry (GC-MS). We identified the pigments in order to assess chronological inconsistency (anachronistic pigments) with the work of the Spanish artist Pablo Picasso (1881–1973) by means of in situ and cross-section analyses by mRS. Using mRS we identified the pigments ‘phthalocyanine blue’, ‘phthalocyanine green’, ‘pyrazolone orange’, ‘anatase’ and ‘rutile’ (titanium dioxide). These results were corroborated by SEM/EDX elemental analysis, which detected Ba, S and Zn among others, so prompting discussion about the use of ready-mixed house paints (Ripolin®). The ground layer was also investigated by mRS, which confirmed the use of rutile (titanium dioxide), calcite and phyllosilicates (Al, Fe). mRS on the white area identified the binding media as beeswax, the most important wax used in art. ATR-FTIR and GC-MS analysis support the presence of a wax and an oil–resin mixture as the binder, described in previous research as being used by Picasso. All the artist materials identified were widely used in art at the beginning of the twentieth century according to the available bibliography and are therefore consistent with the Picasso era. To the best of our knowledge this is the first attempt to investigate a painting related to Picasso using the combination of analytical techniques proposed here.

A comprehensive analysis of the effectiveness of the electrode potential (EV) in tuning the energies of the electronic states (E) of hybrid systems composed by molecules (A) bonded to discrete metal clusters (M) is carried out for the first time by combining experimental SERS data with TDDFT calculations on [Mn-A]q complexes of different sizes (n) and charges (q). It will be demonstrated that the unexplained origin of observed huge energy gains up to G = 5 eV/V involves two different contributions: G = ΔE/ΔEV = SC. The first one is responsible for the effect of a fractional charge (qeff = q/n) on the electronic structure of [Mn-A]q complexes which tunes the CT states through the slopes S of the E vs qeff diagrams. The second contribution (C = Δqeff/ΔEV) is a kind of capacitance that quantifies the ability of the metal to convert the electrode potential EV into the atomic excess of charge qeff. The estimated capacitances of nanometer-size SERS active hot spots are 2 or 3 times larger than those measured fr...

The first page of this article is displayed as the abstract., Rohit Chikkaraddy opened the discussion of the Introductory Lecture: Regarding quantifying the chemical enhancement, you showed a systematic change in the SERS enhancement for halide substituted molecules due to charge transfer from the metal. Is the extra enhancement due to an inherent increase in the Raman cross-section of the molecule? How do you go about referencing, as the charge transfer changes the vibrational frequency? Richard Van Duyne answered: The extra enhancement is not due to an increase in the Raman cross section, as that is ratioed out in the calculation of the enhancement factor. The charge transfer (CT) process does not transfer a complete electron, it is a fractional degree of CT. Thus the change in vibrational frequency is small. DFT calculations that provide eigenvectors allow one to reference the vibrational modes of the free molecule with those of the adsorbed molecule. Sylwester Gawinkowski asked: You have shown that the enhancement factor curve is redshifted relative to the plasmon resonance band and has a maximum at about 800 nm. This means that the SERS signal should be strongest for excitations in the near infrared spectral region. Why do most SERS reports, particularly related to single molecule SERS, have the excitation in the green or red spectral range and not in the near infrared?

Breast cancer is the second most common type of cancer worldwide and the most frequent among women, being the fifth cause of death from neoplastic disease. Since this is an oxidative-stress related neoplasia, it is largely preventable. A dietary isoflavone abundant in soybean - daidzein - is currently being investigated owing to its chemopreventive and/or chemotherapeutic properties towards the human MDA-MB-231 (metastatic, estrogen-unresponsive) and MCF-7 (estrogen-responsive) breast cancer cell lines. Biological assays for evaluation of antitumour and anti-invasive activities were combined with state-of-the-art vibrational microspectroscopy techniques. At 50 and 100 μM concentrations and 48 h incubation time, daidzein was found to induce a marked decrease in cell viability (ca. 50%) for MDA-MB-231 and MCF-7 cells (respectively ca. 50% and 42%) and 40% inhibition of cell migration. MicroRaman analysis of fixed cells upon exposure to this isoflavone unveiled its metabolic impact on both cell lines. Multivariate data analysis (unsupervised PCA) led to a clear discrimination between the control and DAID-exposed cells, with distinctive effects on their biochemical profile, particularly regarding DNA, lipids and protein components, in a cell-dependent way. This is the first reported study on the impact of dietary antioxidants on cancer cells by microRaman techniques.

The chemical changes associated to the autooxidation process of linoleic acid (LA) were detected by Raman spectroscopy and interpreted in the light of density functional theory (DFT) calculations performed for both the fatty acid and its main oxidation products. The present methodology, applied for a six-day period upon induction of oxidation (through heating), allowed to understand the chemical modifications occurring during the oxidation process. Raman spectroscopy was shown to be a suitable and reliable technique for assessing the oxidation degree of fatty acid samples, particularly pure fatty acids, mainly when computational methods are used alongside to predict the spectral features of the distinct chemical entities involved. Screening of the oxidation process was mostly based on the loss of intensity of the bands assigned to LA cis-double bonds. Copyright © 2012 John Wiley & Sons, Ltd.

The photodissociation of methyl thionitrite (CH 3 SNO) has been computationally studied by means of CAS-SCF and MS-CASPT2 methods. The analysis of the multiconfigurational wavefunction corroborates the assignments of the absorption spectra, the visible and UV bands assigned to S 0 → S 1 (n, π ∗ ) and S 0 → S 2 (π, π ∗ ) transitions correspond to 1A′ → 1A″(n σ , π ∗ ) and 1A′ → 2A′(n π , π ∗ ) excitations, respectively. With respect to the photochemistry of CH 3 SNO, it is found that the potential energy surfaces associated with the low-lying excited states of this molecule (1 1 A″, 2 1 A′, and 2 1 A″) are repulsive along the NO elimination coordinates. For this reason, population of such excited states leads to NO extrusion as the primary process, in agreement with experiments.

Chromone and two carboxylic derivatives – chromone-2-carboxylic acid (2CA) and chromone-3-carboxylic acid (3CA) – were investigated as to their conformational preferences by vibrational spectroscopy – Raman, FTIR and INS – combined to density functional theory and plane-wave calculations. INS experiments allowed to clearly detect intramolecular hydrogen-type close contacts in these systems. A natural bond orbital (NBO) analysis was performed, including calculation of the second-order perturbation energies ( E (2) ) and orbital occupancies, to provide theoretical evidence of the stabilisation due to the π i * → π j * donor–acceptor interaction. A complete assignment of the vibrational spectra was achieved for all compounds, allowing us to determine their most stable conformers and establish their H-bonding profile. 3CA was shown to display a particularly strong intramolecular H-bond, which can explain its singular conformational behaviour and abnormally high p K a value.

The analysis of photoinduced charge transfer (CT) processes in a particular SERS spectrum is not a trivial task since each system must be studied separately and no universal selection rules can be proposed for this kind of enhancement mechanism. Despite this, we found out in previous studies that the SERS-CT spectra of benzene-like molecules are mainly characterized by the strong enhancement of the totally symmetric 8a ring-stretching vibration and we have used this as a propensity rule to recognize the presence of resonant CT processes in the SERS of these adsorbates. However, it is necessary to cautiously consider the relevant symmetry of the system under study before applying this simplified rule. When the molecule shows a low symmetry (or the relevant symmetry is reduced by the adsorption on the metal as it was demonstrated in the case of pyrimidine), the selective intensification of the 8a mode can be disguised by the redistribution of the CT enhancement with another close vibration in wavenumber, na...

The Surface-enhanced Raman scattering of benzenesulfonamide and sulfanilamide adsorbed on silver sols was studied. On the basis of the noticeable shifts observed for wavenumbers of the νs(OSO), ν(CS), and ν(SN) vibrations with respect to the Raman spectra of the solids and the ionic solutions, we conclude that these molecules are adsorbed on silver nanoclusters at pH ≥ 7 with the aminosulfonyl groups partially deprotonated. The benzenesulfonamide links to the metal through the nitrogen atom of the corresponding azanion, while the sulfanilamide interacts in turn through the nitrogen atoms of the –NH2 and –SO2NH– groups in the para-position. Additionally, it was found that the most enhanced surface-enhanced Raman scattering bands, especially the 8a;νring mode, are related to the presence of the charge transfer mechanism. Copyright © 2011 John Wiley & Sons, Ltd.

A SERS study of chromone 3-carboxylic acid adsorbed on silver colloids was undertaken, in order to assess the ability of this compound to accept electrons in charge transfer (CT) processes. Theoretical SERS intensities under photoinduced CT resonant conditions have been carried out for both the neutral and the deprotonated species allowing to conclude, by comparison with the experimental data, that the recorded SER corresponds to the anionic form of the acid linked to the metal. It was shown that the SERS-CT mechanism predominates for this particular compound, thus explaining the strong enhancement of the band at ca. 1600 cm(-1) assigned to the 8a ring stretching mode. The identification of CT processes is of the utmost importance for understanding the mechanism through which these benzopyranes may act as antioxidants.

The molecular mechanism of the reaction of nitroglycerin with a cysteil-cysteine derivative has been studied by quantum mechanical methods; in particular, density functional theory with the accurate meta exchange-correlation functional M06-2X was used. The first reaction step is nitration of a deprotonated cysteine of the dipeptide. Afterward, six reaction steps are followed to yield the final products of the process: 1,2-glyceryl dinitrate (GDN), nitric oxide (NO), peroxynitrite anion (−OONO), and superoxide anion (O2 −) plus an intramolecular disulfide bond in the dipeptide. Two nitroglycerin molecules are decomposed for each disulfide bond formation in the dipeptide. A reducing agent is necessary to complete the global reaction. The action of the reductant triggers S-peroxynitrite formation, which, in turn, can decompose into −OONO or NO plus O2 −.

El diagnóstico anticipado de la enfermedad cardiaca durante la etapa de gestación del feto es uno de los retos de la medicina actual. La evaluación del electrocardiograma fetal es, por tanto, crucial para diagnosticar diversas anomalías cardiacas. No obstante, extraer el electrocardiograma fetal para su posterior valoración es una tarea complicada debido a muchos factores que abarcan desde las técnicas de adquisición del mismo y afección de factores fisiológicos, hasta la posible comorbidad entre diversas patologías.Desde años atrás la investigación en el estudio del electrocardiograma fetal y se han empleado técnicas tanto invasivas como no invasivas. La técnica no invasiva más usada es el ultrasonido Doppler pero éste no aporta información respecto a los parámetros morfológicos y temporales del electrocardiograma fetal; este último puede obtenerse mediante la colocación de eléctrodos sobre el abdomen y el tórax de la madre. Esta técnica abre la posibilidad de caracterizar la señal del electrocardiograma fetal; el problema radica en que la señal se mezcla con otras señales biomédicas, como la del electrocardiograma materno, la respiración, la actividad estomacal y las contracciones del útero, y por interferencias externas provocadas por la red eléctrica o el ruido térmico. Al día de hoy la señal del electrocardiograma fetal está aún en etapa de caracterización, motivo por el cual se hace necesario investigar nuevas metodologías para su estudio.El objetivo de este trabajo es utilizar técnicas de procesamiento de señales para extraer de manera no invasiva el electrocardiograma fetal partiendo del electrocardiograma superficial de la madre a fin de obtener una estimación de la frecuencia cardiaca fetal.Early fetal diagnosis of heart disease during pregnancy is one of the current medical challenges. Therefore, the evaluation of the fetal electrocardiogram is crucial in the diagnosis of various cardiac abnormalities. However, the performance of the fetal electrocardiogram for its further assessment is a complicated task due to many factors ranging from EEG acquisition techniques and conditions of physiological factors, to the possible comorbidity between different pathologies.From years ago, the scientific investigation is focused in the study of the fetal electrocardiogram and both invasive and non-invasive techniques have been used. The non-invasive most used technique is the doppler ultrasound, but this does not provide information about the morphological and temporal parameters of the fetal electrocardiogram; the latter can be obtained by placing electrodes on the abdomen and thorax of the mother. This technique opens the possibility to characterize the fetal electrocardiographic signal but there is the problem that this signal may be mixed with other bio-medical signals such as maternal ECG,respiration, stomach activity, contraction of the uterus, and by external interference with AC power or thermal noise. As of today, the fetal electrocardiographic signal is still in a characterization stage, which is why it is necessary to investigate new methodologies for its study.The aim of this work is to use signal processing techniques to perform a non-invasive fetal electrocardiogram starting from the superficial electrocardiogram of the mother in order to obtain an estimate of the fetal heart rate.

Surface-enhanced Raman scattering (SERS) of benzoate recorded on silver electrode have been analyzed on the basis of a charge transfer (CT) enhancement mechanism similar to a resonance Raman (RR) process where a photoinduced electron transfer between a metal and an adsorbate takes place. Given that benzoic acid (BzH) is adsorbed on silver as benzoate anion (Bz−), this resonant CT process implies the transient formation of the corresponding radical dianion (Bz•2−). The dependence of the relative SERS intensities on the electrode potential has been analyzed on the basis of ab initio calculations of the electronic properties of the isolated adsorbate in its ground and excited CT states (Bz − and Bz•2−, respectively). Moreover, configuration interaction singles (CIS) calculations have also been carried out for the Ag2−benzoate (Ag2−Bz−) supermolecule, which shows two excited singlets, namely CT0;1B1 and CT1;1A2, where the properties of the adsorbate are quite similar to those of the radical dianion of the iso...

Surface enhanced raman scattering (SERS) of triphenylene (TP) has been recorded on Ag nanoparticles functionalized with the molecular assembler bis-acridinium lucigenine dication (LG) which approaches the adsorbate to the metal surface allowing for its detection. Structural information on the host and the analyte can be extracted from the SERS spectra of LG and LG/TP complex. The acridinium planes in LG are staggered, so cavities into which hydrophobic TP can be allocated are created. Moreover, the orientation of LG with respect to the metal surface changes from tilted to perpendicular when concentration of TP increases. However, perpendicular orientation of TP with respect to the metal surface is preferred according to the in-plane enhanced bands recorded in the SERS spectrum. The dependence of the Raman signal of TP on LG concentration has been checked, and trace concentrations of TP have been detected by this technique which therefore can be used as a chemical sensor of organic pollutants.

To help understand the mechanism of chemical peeling of boron nitride nanotubes, single-walled model systems have been studied using Density Functional Theory. Dimethyl sulfoxide acts as a water tr...

Surface-enhanced Raman scattering (SERS) of hydroxybenzoic acids has been studied on silver sols in H(2)O and D(2)O solutions. The adsorption behavior of 4-hydroxybenzoic acid (4HBA) is different from that of salicylic (2HBA) and 3-hydroxybenzoic (3HBA) acids. It was concluded that 4HBA is adsorbed on silver nanoparticles (Ag(n)) as either oxidobenzoate (A(2-)) or hydroxybenzoate (A(-)), depending on the pH of the solution, given rise to a flat orientation. Both 2HBA and 3HBA acids are always adsorbed as hydroxybenzoates anions (A(-)) at pHor=5 and link to the metal through the carboxylate group (Ag(n)--A(-)), standing more or less perpendicular to the metal surface. In the case of these monoanions, the selective enhancement of the bands is due mainly to a resonant electron or charge transfer process (ET or CT) from the metallic nanoparticles to the adsorbates, yielding the transient formation of the respective radical dianions (Ag(+)(n)--A(2-)). It is found that the enhanced bands, and especially the mode 8a;nu(ring), are related to the difference between the equilibrium structures of the adsorbate in its ground (A(-)) and CT-excited (A(2-)) states. In the SERS spectrum of 4HBA dianion, the contribution of CT mechanism is not observed.

The surface-enhanced Raman scattering (SERS) of p-benzoquinone (Q) adsorbed on silver nanoclusters (Agn) reported by Tripathi (J. Am. Chem. Soc. 2003, 125, 1179) is analyzed by means of high-level ab initio calculations. CASPT2 energies of the Ag2−Q model confirm the charge transfer character of the adsorption (Agn + Q → Agn+−Q−•), yielding the semiquinone radical anion (Q−•). On the contrary, we demonstrate that the selective enhancement shown by mode 7a in SERS is due to a resonant process between the 2B2g ground state and the 2Au excited doublet of Q−•. This is an unexpected result given that the electronic spectrum is dominated by the strong dipole-allowed 2B2g → 2B3u transition. Therefore, that spectrum is, to our knowledge, the only reported surface-enhanced resonance Raman scattering spectrum involving two doublet states of an adsorbate.

SERS of trans -3-hydroxycinnamic acid adsorbed on silver colloids have been analyzed in order to detect resonant charge transfer processes similar to a resonance Raman mechanism, involving the photoinduced transfer of an electron from the metal to the adsorbate (SERS-CT). Theoretical SERS-CT intensities for the neutral, anionic and dianionic forms have been calculated and it was found that the active SERS species corresponds to cinnamate ion linked to the metal through its carboxylate group. Moreover, it has been shown that the SERS-CT mechanism is operating in the SERS, explaining the strong enhancement of the band at ca. 1600 cm −1 , assigned to the 8a mode.

The photochemical behavior of the protonated simplest nitrosamine [NH2NO-H](+) has been addressed by means of the CASPT2//CASSCF methodology in conjunction with the ANO-L basis sets. The relative stability of the different tautomers, namely, (1) NH2NOH(+), (2) NH3NO(+), and (3) NH2NHO(+), has been considered, and the corresponding tautomerization transition states have been characterized. With respect to the most chemically relevant species, it has been found that NH2NOH(+) corresponds to a bound structure, while NH3NO(+) corresponds to an adduct between NH3 and NO(+) at both CASSCF and CASPT2 levels of theory. Vertical transition calculations and linear interpolations on the homolytic dissociation of NH3NO(+) in combination with previous results on neutral nitrosamine [J. Chem. Phys. 2006, 125, 164311] and neutral N,N-dimethylnitrosamine [J. Org. Chem. 2007, 72, 4741] indicate that, in acidic diluted solutions, the protonation of nitrosamine takes place on the excited surface. The N-N dissociation channels have been studied both in ground and first excited singlet state. An S1/S0 conical intersection is found to be responsible for the photostability of NH2NOH(+). On the contrary, NH3NO(+) is photochemically unstable as its first excited state is purely dissociative. The latter species is characterized by a twofold reactivity: the formation of nitrosyl cation (NO(+)) in the ground state and the photorelease of physiologically relevant nitric oxide radical (NO) in its first excited state.

Molecular planarity of penta-p-phenylene (P5P) and several substituted derivatives with four side chains of various lengths, including deca(ethylene glycol) groups, is discussed by considering the changes in the intensity ratio between the Raman bands recorded at 1280 and 1220 cm(-1). The intensity ratio between both bands I(1280)/I(1220) shows a small increase with the size of the substituent, indicating a high rigidity for all these compounds, even those with long oligo(ethylene glycol) side chains. This result is important given that these phenylene derivatives are versatile building blocks for the construction of nanometric tripod-shaped adsorbates for biological applications since the side chains should prevent the nonspecific interaction with proteins.

7 págs.; 5 figs.; 1 app. Supplementary material, Surface-Enhanced Raman Spectra (SERS) of methyl N-(1H-benzimidazol-2-yl)carbamate (MBC), usually named carbendazim, have been recorded on silver colloids at different pH values. In order to identify the neutral, protonated or deprotonated species of MBC that originate the SERS, the vibrational wavenumbers of these three isolated forms and linked to a silver atom have been predicted by carrying out DFT calculations. The results indicate that the active SERS species in the studied pH range correspond to the neutral MBC and its deprotonated ion in the amidate form. According to theoretical calculations, neutral MBC is linked to the metal through the imidazolic nitrogen atom, while the deprotonated MBC could be linked through the imidazolic nitrogen together with the amidic nitrogen atom or the carbonyl oxygen atom. Both adsorbed species, neutral and deprotonated, have the benzimidazolic ring orientated almost perpendicular to the silver surface and no molecular reorientation has been detected. pH of the bulk controls the relative abundance of the neutral MBC and its amidate anion which can be monitored through the intensities of the SERS bands recorded at about 1230 and 1270cm. These two key bands correspond to the in-plane NH deformation of amidic and imidazolic groups, respectively. 2015 Elsevier Inc. All rights reserved., We are grateful to the Spanish MINECO (CTQ2012-31846, FIS2014-52212-R) and Junta de Andalucía (FQM-5156 and 6778), and to the Brazilian agencies CAPES, CNPq and FAPESP, for financial support. The authors thank to SCAI and Rafael Larrosa (UMA) for computational facilities.

Potential energy surfaces, minimum energy reaction paths, minima, transition states, reaction barriers, and conical intersections for the most important atmospheric reactions of methyl nitrate (CH(3)ONO(2)) and methylperoxy nitrite (C(3)HOONO) on the electronic ground state have been studied (i) with the second-order multiconfigurational perturbation theory (CASPT2) by computation of numerical energy gradients for stationary points and (ii) with the density functional theory (DFT). The proposed mechanism explains the conversion of unreactive alkyl peroxy radicals into alkoxy radicals: CH(3)O(2) + NO=CH(3)OONO=CH(3)O + NO(2) left arrow over right arrow CH(3)ONO(2). Additionally, several discrepancies found in the comparison of the results obtained from the two employed approaches are analyzed. CASPT2 predicts that all dissociation reactions into radicals occur without an extra exit energy barrier. In contrast, DFT finds transition states for the dissociations of cis- and trans-methylperoxy nitrite into CH(3)O + NO(2). Furthermore, multiconfigurational methods [CASPT2 and complete active space SCF (CAS-SCF)] predict the isomerization of CH3ONO2 to CH3OONO to occur in a two-step mechanism: (i) CH(3)ONO(2) --CH(3)O + NO(2); and (ii) CH(3)O + NO(2) --CH(3)OONO. The reason for this has to do with the coupling of the ground electronic state with the first excited state. Therefore, it is demonstrated that DFT methods based on single determinantal wave functions give an incorrect picture of the aforementioned reaction mechanisms.

Aromatic amino groups can be attached through different binding points to the surface. In a previous work, we have demonstrated that α-phenylglycine (PGly) interacts with a silver surface through its functional groups. In addition, a large charge-transfer (CT) contribution was found in the overall SERS intensification. In the present work we studied the SERS of PGly on Ag metal colloids prepared by different methods in order to investigate the influence of the chemical nature of the metal substrate on the adsorption and on the CT processes taking place between this amino acid and the metal.